1. Field of the Invention
This invention relates generally to electronic telecommunication systems, and relates more particularly to an apparatus and method for efficiently implementing a satellite transceiver system.
2. Description of the Background Art
An efficient and cost-effective implementation is generally a significant consideration for manufacturers, designers, and users of modern telecommunication systems. A telecommunication system that successfully combines both efficiency and cost-effectiveness may therefore advantageously provide substantial economic benefits and achieve effective functionality.
Referring now to FIG. 1, a diagram for an installation of a conventional satellite transceiver system is shown. The installation of FIG. 1 includes a shelter 110, an antenna 112, an outdoor unit (ODU) 114, an indoor unit (IDU) 116, and a user interface 118. The FIG. 1 system is preferably designed for use as a Single Subscriber Satellite Communications Terminal that may typically be used for various telecommunication applications, such as rural telephony.
In operation, a user may enter shelter 110 and utilize user interface 118 to communicate with other subscribers of the telecommunication system. User interface 118 typically includes a user headset and a keypad to allow a system user to access the telecommunication system. IDU 116 may include a modem, a coder/decoder, power supplies, and control circuitry. ODU 114 typically includes an up-converter, a power amplifier, a down-converter, and a multiplexer. Therefore, a user may access the FIG. 1 system via user interface 118, IDU 116, ODU 114, and antenna 112 to either transmit or receive selected information. In practice, the FIG. 1 system exhibits reduced efficiency and cost-effectiveness because the ODU 114 and the IDU 116 are divided into two separate installation locations.
Referring now to FIG. 2, a drawing of a Cartesian graph showing values for an offset quaternary phase shift keying (OQPSK) modulation scheme is shown. In contemporary telecommunications, selected information to be transmitted to a satellite may be imposed onto a microwave carrier using various efficient modulation schemes including OQPSK.
In a Cartesian graph having Cartesian coordinates, any point on an analog waveform may be represented by X and Y coordinates. In Cartesian symbology, the X coordinate is called I, and the Y coordinate is called Q. In the FIG. 2 graph depicting an OQPSK modulation scheme, different values for I and Q may thus be combined to represent two bits of digital data. For example, a binary value of 00 may be represented by vector 216 and coordinates 218. Similarly, coordinates 222 correspond to a binary value of 01, coordinates 226 correspond to a binary value of 10, and coordinates 230 correspond to a binary value of 11.
As illustrated in FIG. 2 by dotted lines 220, 224, and 228, whenever the two-bit binary values change, the corresponding vector 216 must vary its amplitude to directly traverse to a new set of coordinates. Any distortion or error in the amplitude of vector 216 may introduce potential error in the binary values corresponding to the related coordinates. For the foregoing reasons, contemporary advanced modulation schemes like OQPSK require the use of highly linear power output amplifiers in the transmitter section of a satellite transceiver to avoid distortion in the transmitted data signal and corresponding loss of transmitted data.
The requirement for highly linear power amplifiers conventionally predicates the use of very high performance power amplifiers operating at high current levels. This mode of operation results in significant reduction of costeffectiveness in the overall system functionality. The foregoing problems are compounded because satellite transceivers typically function at higher operating frequencies which place greater demands and constraints on the overall transceiver system design. Therefore, for all the foregoing reasons, an improved apparatus and method are needed for efficiently implementing a satellite transceiver system.